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United States Patent |
5,025,064
|
Reiff
,   et al.
|
June 18, 1991
|
Process for the production of aqueous polyurethane dispersions
Abstract
The present invention relates to a process for the production of aqueous
dispersions of polyurethanes containing chemically incorporated
carboxylate groups wherein the counterions to the carboxylate groups are
predominantly ammonium ions corresponding to the formula
##STR1##
by mixing a starting aqueous dispersion of polyurethanes containing
chemically incorporated carboxylate groups wherein the counterions to the
carboxylate groups are ammonium ions corresponding to the formula
##STR2##
wherein R.sub.1, R.sub.2 and R.sub.3 are the same or different and
represent C.sub.1-4 alkyl groups, provided that the total number of carbon
atoms in these substituents is 3 to 6,
with at least an equivalent quantity of ammonia, based on the trialkyl
ammonium ions, and subsequently removing under vacuum at least a portion
of the displaced trialkyl amines and the excess ammonia, if present.
Inventors:
|
Reiff; Helmut (Leverkusen, DE);
Lorenz; Otto (Roetgen, DE)
|
Assignee:
|
Bayer Aktiengesellschaft (Leverkusen, DE)
|
Appl. No.:
|
547273 |
Filed:
|
July 3, 1990 |
Foreign Application Priority Data
Current U.S. Class: |
524/591; 524/839; 524/840 |
Intern'l Class: |
C08L 075/04 |
Field of Search: |
524/591,839,840
|
References Cited
U.S. Patent Documents
3479310 | Nov., 1969 | Dieterich et al. | 260/29.
|
4092286 | May., 1978 | Noll et al. | 250/29.
|
4237264 | Dec., 1980 | Noll et al. | 528/67.
|
4408008 | Oct., 1983 | Markusch | 524/591.
|
4764553 | Aug., 1988 | Mosbach et al. | 524/591.
|
Foreign Patent Documents |
1076688 | Jul., 1967 | GB.
| |
Primary Examiner: Welsh; Maurice J.
Attorney, Agent or Firm: Gil; Joseph C., Roy; Thomas W.
Claims
What is claimed is:
1. A process for the production of an aqueous dispersion of polyurethanes
containing chemically incorporated carboxylate groups wherein the
counterions to the carboxylate groups are predominantly ammonium ions
corresponding to the formula
##STR9##
which comprises mixing a starting aqueous dispersion of polyurethanes
containing chemically incorporated carboxylate groups wherein the
counterions to the carboxylate groups comprise ammonium ions corresponding
to the formula
##STR10##
wherein R.sub.1, R.sub.2 and R.sub.3 are the same or different and
represent C.sub.1-4 alkyl groups, provided that the total number of carbon
atoms in these substituents is 3 to 6,
with at least an equivalent quantity of ammonia, based on the trialkyl
ammonium ions, and subsequently removing under vacuum at least a portion
of the displaced trialkyl amines and the excess ammonia, if present.
2. The process of claim 1 wherein said starting aqueous dispersion contains
anionically modified polyurethanes having 0.1 to 120 milliequivalents per
100 g of solids of carboxylate groups in the form of incorporated
structural units corresponding to the formula
##STR11##
wherein R is a C.sub.1-4 alkyl radical.
3. The process of claim 1 wherein ammonia is used in the form of an aqueous
ammonia solution.
4. The process of claim 2 wherein ammonia is used in the form of an aqueous
ammonia solution.
5. The process of claim 1 wherein said polyurethanes contain a positive
amount of up to 30% by weight of ethylene oxide units present in terminal
or lateral polyether chains.
6. The process of claim 4 wherein said polyurethanes contain a positive
amount of up to 30% by weight of ethylene oxide units present in terminal
or lateral polyether chains.
7. The process of claim 1 wherein R.sub.1, R.sub.2 and R.sub.3 represent
ethyl groups.
8. The process of claim 2 wherein R.sub.1, R.sub.2 and R.sub.3 represent
ethyl groups.
9. The process of claim 4 wherein R.sub.1, R.sub.2 and R.sub.3 represent
ethyl groups.
10. The process of claim 6 wherein R.sub.1, R.sub.2 and R.sub.3 represent
ethyl groups.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a new process for the production of aqueous
dispersions of polyurethanes containing chemically incorporated
carboxylate groups wherein the counterions to the carboxylate groups are
predominantly unsubstituted ammonium groups.
2. Description of the Prior Art
Aqueous dispersions of polyurethanes containing chemically incorporated
carboxylate groups as hydrophilic centers are known (cf. for example DE-AS
1 495 745 (U.S. Pat. No. 3,479,310), GB-PS 1,076,688, U.S. Pat. No.
4,092,286, U.S. Pat No. 4,237,264 or U.S. Pat. No. 4,408,008).
In these known dispersions, ammonium cations derived from tertiary amines
are generally present as counterions to the chemically incorporated
carboxylate groups. For example, it is expressly recommended in U.S. Pat.
No. 4,408,008 (column 9, line 46 to column 10, line 1) to use amines with
no isocyanate-reactive hydrogen atoms to neutralize the carboxyl groups in
the production of aqueous polyurethane dispersions. The advantage of using
readily volatile tertiary amines to neutralize the chemically incorporated
carboxyl groups is that the amines diffuse off during the production of
coatings from the polyurethane dispersions which increases the resistance
of the coatings to water vapor. The disadvantage of readily volatile
tertiary amines is that they are neither ecologically nor toxicologically
desirable.
Accordingly, a considerable advance is embodied in the dispersions of
polyurethanes containing carboxylate groups described in EP-A-0 269 972
which contain ionic hydrophilic centers corresponding to the formula
##STR3##
wherein R is a C.sub.1-4 alkyl radical.
In contrast to Example 11 of DE-AS 1 495 745, which describes the
production of a dispersion containing ammonium groups as counterions which
is unsatisfactory for many applications, the dispersions according to
EP-A-0 269 972 are high quality products whose only disadvantage is the
disclosed process for their production. Thus, in the production of the
polyurethanes, only very special hydroxycarboxylic acids can be used to
incorporate the ionic centers such as dimethylol propionic acid. The
hydroxyl groups of these special hydroxycarboxylic acids react selectively
with isocyanates to form urethanes without the carboxyl groups
participating in the reaction so that, after production of the
polyurethanes, they can be converted into carboxylate groups by
neutralization. In addition, in the production of the polyurethanes, the
isocyanate polyaddition reaction has to be complete before the carboxyl
groups are neutralized with ammonia to avoid any reaction between the
isocyanate groups and ammonia. For the same reason, polyhydroxycarboxylic
acids cannot be used in salt form as ionic synthesis component.
A particularly simple process has now been found for the production of
aqueous dispersions of polyurethanes containing incorporated carboxylate
groups in which ammonium groups
##STR4##
are present as counter-ions.
The process according to the invention, which is described in detail
hereinafter, is based on the surprising observation that, despite their
comparatively high boiling point, the tertiary amine counterions present
in the starting dispersions can be replaced with unsubstituted ammonium
groups by treatment of the aqueous dispersions with ammonia and subsequent
removal of the excess base by distillation under vacuum.
SUMMARY OF THE INVENTION
The present invention relates to a process for the production of aqueous
dispersions of polyurethanes containing chemically incorporated
carboxylate groups wherein the counterions to the carboxylate groups are
predominantly ammonium ions corresponding to the formula
##STR5##
by mixing a starting aqueous dispersion of polyurethanes containing
chemically incorporated carboxylate groups wherein the counterions to the
carboxylate groups are ammonium ions corresponding to the formula
##STR6##
wherein
R.sub.1, R.sub.2 and R.sub.3 are the same or different and represent
C.sub.1-4 alkyl groups, provided that the total number of carbon atoms in
these substituents is 3 to 6,
with at least an equivalent quantity of ammonia, based on the trialkyl
ammonium ions, and subsequently removing under vacuum at least a portion
of the displaced trialkyl amines and the excess ammonia, if present.
DETAILED DESCRIPTION OF THE INVENTION
Any aqueous dispersions of polyurethanes containing incorporated
carboxylate groups having ammonium counterions obtained by the addition of
a proton to a tertiary aliphatic amine having 3 to 6 carbon atoms are
suitable as starting dispersions for the process according to the
invention. Accordingly, ammonium ions corresponding to formula III,
wherein R.sub.1, R.sub.2 and R.sub.3 represent alkyl groups as previously
defined, preferably methyl or ethyl groups and more preferably ethyl
groups, are present as counterions to the chemically incorporated
carboxylate groups in the dispersions used as starting materials.
The counterions for the carboxylate groups may be obtained by the addition
of a proton onto an aliphatic amine such as trimethylamine, triethylamine,
N-methyl-N-ethyl propylamine, N,N-dimethyl-ethylamine,
N,N-diethyl-methylamine or N,N-dimethyl-n-butylamine, preferably
trimethylamine or triethylamine and more preferably triethylamine.
Apart from this limitation on the type of counterion, the process according
to the invention may be carried out using any of the aqueous polyurethane
dispersions known from the prior art. Examples include the aqueous
polyurethane dispersions containing carboxylate groups of the type
mentioned as the only hydrophilic groups as described in U.S. Pat. No.
3,479,310 (herein incorporated by reference) or GB-PS 1,076,688, and also
those which, in addition to anionic groups, contain ethylene oxide units
present in terminal or lateral polyether chains as further hydrophilic
groups. These aqueous polyurethane dispersions may be obtained, for
example, in accordance with U.S. Pat. No. 4,092,286, U.S. Pat. No.
4,190,566, U.S. Pat. No. 4,237,264, U.S. Pat. No. 4,192,937, U.S. Pat. No.
4,269,748 or U.S. Pat. No. 4,408,008 (all of the preceding U.S. patents,
herein incorporated by reference) or DE-OS 2 725 589 (U.S. Pat. No.
4,829,122, herein incorporated by reference).
The aqueous polyurethane dispersions to be used in the according to the
invention generally contain 0.1 to 120, preferably 2 to 100
milliequivalents of carboxylate groups chemically incorporated into the
polyurethane per 100 g of solids, and 0 to 30, preferably 0.5 to 10% by
weight of ethylene oxide units present in terminal or lateral polyether
chains, provided that the total content of hydrophilic groups is
sufficient to ensure the dispersibility of the polyurethanes in water. The
counterions to the carboxylate groups are the ammonium ions corresponding
to formula III.
Aqueous dispersions of polyurethanes containing carboxylate groups, in
which the ionic groups are contained in structural units corresponding to
the formula IV
##STR7##
wherein
R represents a C.sub.1-4 alkyl radical, preferably a methyl radical and
R.sub.1 to R.sub.3 represent the previously defined groups, are
particularly preferred for the process according to the invention. These
particularly preferred aqueous polyurethane dispersions may be prepared
according to the previously described prior art processes using
dimethylolalkane carboxylic acids corresponding to the formula
##STR8##
wherein R is a C.sub.1-4 alkyl group, for the production of the
polyurethanes with subsequent neutralization of the carboxyl groups with
tertiary aliphatic amines containing 3 to 6 carbon atoms or by using the
corresponding salts as an ionic synthesis component in the production of
the polyurethanes.
To carry out the process according to the invention, the aqueous
dispersions generally have a solids content of 5 to 50% by weight. The
continuous phase of the dispersions used in the process according to the
invention is based on water or a mixture of water with an organic solvent
optionally used in the production of the dispersions such as acetone or
N-methyl pyrrolidone. These solvents may optionally be present in the
aqueous dispersions in a quantity of up to 35% by weight, based on the
weight of the continuous liquid phase. When the dispersions are produced
using these organic solvents, the solvents are generally removed by
distillation after production of the dispersions. In accordance with the
present invention the removal of the organic solvent by distillation may
be carried out together with the process according to the invention which
also requires a distillation step.
To carry out the process according to the invention, ammonia is added to
the starting dispersions in an amount sufficient to provide at least 1
mole, preferably 2 to 15 moles and more preferably 3 to 8 moles of ammonia
for every mole of counterions corresponding to formula III present in the
dispersions. The ammonia may be introduced into the dispersion in gaseous
form. However, the ammonia is preferably used in the form of a 1 to 25% by
weight, preferably 5 to 15% by weight aqueous solution at a temperature
from room temperature to 80.degree. C.
After the ammonia has been added, the dispersion is generally stirred for
15 minutes to 18 hours, followed by removal of the excess base by
distillation under vacuum at a temperature of 10.degree. to 60.degree. C.
The trialkylamine which is removed by distillation may be recycled for the
preparation of another batch. If desired, the water optionally distilled
off at the same time is at least partly replaced by the addition of more
water to establish the desired solids content in the ready-to-use
dispersion. In embodiments where the aqueous dispersions also contain low
boiling organic solvents, these solvents may also be substantially removed
by distillation at the same time as the removal of the excess base by
distillation.
In accordance with the present invention it is possible in a single step to
obtain aqueous dispersions of polyurethanes containing incorporated
carboxylate groups, wherein at least 50 equivalent-% and preferably at
least 75 equivalent-% of the counterions consist of ammonium ions
corresponding to formula II. If desired, the described process may be
repeated as often as necessary to complete the cation exchange.
It must be regarded as particularly surprising that it is possible by this
simple method to substantially replace the trialkylamines with ammonia
because the trialkylamines are relatively strong bases and, in addition,
have distinctly higher boiling points than ammonia.
The products obtained in accordance with the process of the present
invention are valuable coating compositions for any substrates. Ammonia
escapes during drying of the coatings.
In the following examples, all percentages are percentages by weight.
EXAMPLES
Preparation of an aqueous polYurethane dispersion I
Starting materials
______________________________________
200 g polypropylene glycol, molecular weight 2,000
10.4 g dimethylol propionic acid
7.1 g of a monohydric polyether alcohol having an OH
number of 26 and prepared by the alkoxylation of
n-butanol using a mixture of 83% ethylene oxide
and 17% propylene oxide
87.3 g 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl
cyclohexane (IPDI)
48.1 g caprolactam
7.9 g triethylamine
830 g deionized water
______________________________________
Procedure
Dimethylene propionic acid and the dehydrated polyethers were initially
introduced and reacted with IPDI at 80.degree. to 105.degree. C. After 90
minutes, caprolactam was added, followed by stirring for another 60
minutes at 105.degree. C. The triethylamine was added dropwise at
100.degree. C., followed by stirring for 3 to 5 hours at 100.degree. C.
until no more isocyanate could be detected by infrared analysis. The
reaction product was then dispersed in water over a period of 8 minutes
and the resulting dispersion was cooled to room temperature. Approximately
1200 g of a finely divided, storage stable polyurethane dispersion were
obtained.
The polyurethane dispersion had carboxylate group content of 21.4
milliequivalents (meq) per 100 g solids, a content of ethylene oxide units
of 1.6%, a pH value of 8 and a solids content of 30% (calculated).
Preparation of an aoueous polyurethane dispersion II
38.8 g (0.231 moles) of 1, 6-diisocyanatohexane were added at 50.degree. C.
to a dehydrated mixture of 248 g (0.146 moles) of a hexanediol/neopentyl
glycol adipate (molar ratio of glycols 1:1) and 12.5 g of an
n-butanol-initiated polyethylene oxide/polypropylene oxide polyether
(EO:PO ratio 85:15) having a molecular weight 2300. After heating for 2
hours to 105.degree. C., the NCO-terminated prepolymer was dissolved in
770 ml acetone. The NCO content was 1.85% by weight.
The solution was then stirred with 37.4 g (0.064 moles) of a 40% aqueous
solution of the triethylamine salt of N-aminoethyl-B-aminopropionic acid
in 50 ml water. After 15 minutes, the product was dispersed with 640 ml
water and the acetone was distilled off resulting in a very finely
divided, stable polyurethane dispersion containing triethyl ammonium
carboxylate groups.
______________________________________
Data: quantity: 1000 g
pH value: 6-7
solids content:
30%
COO.sup..theta. content:
20.4 meq/100 g solids
______________________________________
Preparation of an aqueous polyurethane dispersion III
The preparation of polyurethane dispersion II was repeated with the
exception that only 26.9 g (0.046 moles) of the triethylamine salt of
N-aminoethyl-B-aminopropionic acid was used. The resulting polyurethane
dispersion was very similar to polyurethane dispersion II, but contained
only 14.9 meq of carboxylate groups per 100 g of solids.
EXAMPLE 1 (process according to the invention)
32.6 g (115 meq) of a 6% aqueous ammonia solution were added to 500 g of
polyurethane dispersion I which contained 32.1 meq of triethylamine in
protonated form. After stirring for 30 minutes at room temperature, a
mixture of water, triethylamine and ammonia was distilled off under vacuum
at room temperature and condensed in a cold trap. 140 g of condensate
containing 22 meq of triethylamine were obtained which corresponded to an
exchange rate of 67.5 equivalent %.
The dispersion was readjusted to a solids content of 30% by the addition of
140 g water. It had a pH value of 8.3.+-.0.2 and remained stable in
storage for months with no change in the particle size.
EXAMPLE 2 (process according to the invention)
Example 1 was repeated using three times the quantity of the 6% aqueous
ammonia solution (345 meq). The condensate (155 g) contained 28.4 meq of
triethylamine which corresponded to an exchange rate of at least 88.5
equivalent %.
EXAMPLE 3 (process according to the invention)
500 g of polyurethane dispersion II were mixed with 22.7 g of a 25% aqueous
ammonia solution (15-fold excess, based on triethylamine). The mixture was
stirred at room temperature for 2 hours and distilled under vacuum. 170 ml
of distillate containing water, ammonia and triethylamine were obtained in
a receiver cooled with dry ice. The triethylamine content was
quantitatively analyzed and corresponded to a quantity of 86% of the
theoretical. When this example was repeated using polyurethane dispersion
III, a quantity of 81% of the theoretical amount of triethylamine was
obtained in the distillate.
EXAMPLE 4 (preparation of an aqueous polyurethane dispersion and process
according to the invention)
A dispersion was prepared in accordance with the acetone process described
in U.S. Pat. No. 3,479,310 by forming the reaction product of
______________________________________
0.16 moles of a polyester polyol, molecular weight 1740, of
(i) equimolar quantities of adipic acid and phthalic
acid and (ii) ethylene glycol,
0.05 moles dihydroxypolycaprolactone, molecular weight
2000,
0.5 moles 2,2-bis-(4-hydroxycyclohexyl)-propane (BHP),
0.4 moles hexamethylene diisocyanate (HDI)
0.6 moles 3-isocyanatomethyl-3,5,5-trimethyl cyclohexyl
isocyanate (IPDI) and
0.25 moles triethyl ammonium salt of dimethylol propionic
acid,
______________________________________
in the presence of 1945 ml acetone and dispersing the dissolved reaction
product in 1140 g of water.
The dispersed polyurethane had a carboxylate group content of 33.3 meq per
100 g of solids. The particle diameter which was determined from turbidity
measurements, was <20 nm.
The acetone dispersion was stirred overnight at room temperature. It was
then divided into four equal parts to which 6% aqueous ammonia was added
in the amount set forth in the following Table.
After stirring for 30 minutes at room temperature, a mixture of acetone,
water, ammonia and triethylamine was distilled off under vacuum using cold
traps. The triethylamine present in the distillate from the displacement
reaction was quantitatively analyzed. The triethylamine/ammonia exchange
rate was calculated from the quantities found.
The solids content of dispersions 4(a) to 4(d) was adjusted to 30% by the
addition of water. Finely divided, stable, aqueous polyurethane
dispersions were obtained in which the cationic counterions to the
chemically incorporated carboxylate groups were predominantly
unsubstituted ammonium ions, as shown in the following Table.
TABLE
______________________________________
Molar Ratio
of NH.sub.3 Mol-% of --COO.sup.(-) N.sup.(+) H.sub.4 based on total
to N(Et).sub.3
amount of carboxylate group
______________________________________
(4a) 2 54
(4b) 5 76
(4c) 10 81
(4d) 20 92
______________________________________
Although the invention has been described in detail in the foregoing for
the purpose of illustration, it is to be understood that such detail is
solely for that purpose and that variations can be made therein by those
skilled in the art without departing from the spirit and scope of the
invention except as it may be limited by the claims.
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